1. Field of the Invention
The present invention relates generally to texture imagery in computer generated interactive graphics, and more particularly to three dimensional texture imagery in computer generated interactive graphics.
2. Related Art
A typical computer generated image comprises a plurality of polygons. Each polygon may contribute to one or more pixels of the final image (a pixel is a picture element of a display means), wherein each of the pixels may have a unique color based on such attributes as intrinsic color, lighting (specular highlights, shading, shadows, etc.), atmospheric effects (fog, haze, etc.), and texture. As is well known, textures are conventionally used to provide visual detail for polygon surfaces.
Conventional computer image generation systems store varying levels of detail (LOD) of texture data. LOD is described in many publicly available documents, such as "Texture Tile Considerations for Raster Graphics", William Dugan, Jr., et al., SIGGRAPH 1978 Proceedings, Vol. 12#3, Aug. 1978.
FIG. 1A illustrates two dimensional LODs stored for a particular image. LOD[0], also called the base texture, is shown in FIG. 1 as being a two dimensional 8.times.8 texture. The term maplevel.sub.n can be used synonomously with LOD[N], where N is an integer. The base texture LOD[0] is the highest resolution texture that is conventionally stored. LOD n represents the base texture LOD[0] magnified by a factor of 2.sup.-n (other magnification factors could also be used). Thus, LOD[1] is a two dimensional 4.times.4 texture, LOD[2] is a two dimensional 2.times.2 texture, and LOD[3] is a two dimensional 1.times.1 texture.
Most conventional computer graphics systems support two dimensional textures, but not three dimensional textures. A typical texture technique employed in such conventional computer graphics systems is to map a two dimensional grid of texture data to an initially constant color polygon. Systems which support two dimensional textures, but not three dimensional textures, are flawed because they are not capable of solving the frequently-occurring problems wherein data is not planar, but rather is known as a volume. Information resulting from a magnetic resonance imaging (MRI) scan is an example of a volume data set wherein numerous "slices" of data are collected, with all of the slices stacking up to create a volume of data representing the anatomical structure of the scanned area.
A prior approach for supporting three dimensional textures was presented in "Solid Texturing of Complex Surfaces" by Darwyn R. Peachey, Siggraph '85 Proceedings, Volume 19, Number 3, pages 279-286 (1985), which is herein incorporated by reference in its entirety. However, this prior approach is flawed because the concepts discussed therein cannot be implemented to produce a computer graphics system which processes three dimensional textures at interactive rates.
Thus, what is required is a system and method of processing three dimensional textures at interactive rates.